The specific objectives of the proposed study are: 1. To determine the relative proportion of glucanohydrolase producing microorganisms in the plaque and saliva of a selected population of children (0.0DMF as of 1974) using a newly developed microbial culture technique for differentiating bacteria capable of degrading various extracellular glucans. The distribution of these microbes will be correlated with the following data associated with these children: a) the level of cariogenic streptococci and other relevant microorganisms in saliva and site-specific plaque samples, b) the development of carious lesions, and c) a number of epidemiologic variables known or suggested to influence dental caries (age, sex, fluoride exposure, oral hygiene, etc.). 2. To define the oral microorganisms responsible for glucanohydrolase activity. This will be accomplished by: a) systematic bacterial taxonomy, b) studying the physiology of enzyme production with emphasis on examining potential hydrolase inducers compatable with the human metabolism, and c) separating the hydrolytic enzymes involved and determining their substrate specificity. 3. To assess the potential of oral glucanohydrolase producing microorganisms as natural agents to bacterial interference for the colonization of S. mutans. This will be approached in vitro by determining: a) the inhibition of water insoluble polysaccharide formation, and b) the inhibition of adhesions to either glass or specially prepared hydroxyapatite surfaces. An in vivo approach is described using sequential infection of hamsters with glucanohydrolase producing microbes and known cariogenic strains of bacteria.